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[Assembly] Can not execute when encode to shell code .. - Printable Version

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Can not execute when encode to shell code .. - SIM-1866423 - Apr 10, 2015

There my first hello world app with asm(Litle edit,trying bypass null bytes etc..).

PHP Code

<?php 
section .text                                    
    global  _start              
                                      
_start:
    add     edx,len                                 
    mov     ecx,msg             
    add     ebx,1            ;mov     ebx,1               
    add     eax,4            ;mov     eax,4               
    int     0x80                

      xor     ebx,ebx            ;mov     ebx,0               
    mov     al, 1             ;mov     eax,1               
    int     0x80               

section .data                  

msg db      "#Hello World! #B3mB4m",0xa 
len equ     $ - msg 

When ım complie script to executable file, everything going normal.
PHP Code

<?php 
./hello
#Hello World! #B3mB4m 

There dump info ;

PHP Code

<?php 
hello:     file format elf32-i386


Disassembly of section .text:

08048080 <.text>:
 8048080:    83 c2 16                 add    $0x16,%edx
 8048083:    b9 98 90 04 08           mov    $0x8049098,%ecx
 8048088:    83 c3 01                 add    $0x1,%ebx
 804808b:    83 c0 04                 add    $0x4,%eax
 804808e:    cd 80                    int    $0x80
 8048090:    31 db                    xor    %ebx,%ebx
 8048092:    b0 01                    mov    $0x1,%al
 8048094:    cd 80                    int    $0x80 


When im making that shellcode cant execute 😧
Already try to execute in Python/C/C++ ım always get this error ;

PHP Code

<?php 
//System :3.14-kali1-686-pae (32bit)
[php]fragmentation failure 


I'm too hectic right now, sorry for this.So any idea why fail ? 😁

* - LevelUp - Apr 10, 2015

Well firstly you can't utilise your 'message' variable in such a manner because you do not know what is going to be at address because ASLR will randomize that sections base address. You will have to instead utilise a:

Code
_start:
      jmp popme
resume:
      etc etc
      etc etc
popme:
      call resume
      db "#Hello World! #B3mB4m",0x0d,0x0a

Also if you were using this as part of a buffer overflow, it would not work to use 'add <reg32>,0xwhatever' as you've done in your code because you have not zeroed out the registers yet. Instead just use:

Code
xor <reg32>,<reg32>
mov <reg8>,0xwhatever

To be noted that you'll still get a segfault with making that initial change I first suggested because you must disable NX stack first by compiling with -fno-stack-protector -z execstack.

* - SIM-1866423 - Apr 10, 2015

I'm pretty new in asm,asm looks like me little higgledy-piggledy.I will try again, thanks for advice 😉